1. Field of the Invention
This invention relates to a method and apparatus for reducing thermally induced optical distortions in zigzag lasers and amplifiers. More specifically, it relates to an article comprised of a solid state slab laser gain material which has a entrance face and a return face both cut perpendicular with respect to a pump face and having an optical pumping means comprised of diodes with spacing that is tailored at the slab ends to reduce residual end distortions. One embodiment of the invention includes a highly reflective coating bonded to the return face.
2. Description of Related Art
The architecture of most solid state zigzag lasers and amplifiers consists of a slab lasing medium comprised of solid state lasing material having entrance and exit faces cut at Brewster's angle. Beam quality in average power operation has not been good in these lasers. This performance failure is caused by the complementary interplay of different end effects. Slab geometry lasers with zigzag optical paths have been the object of significant research as a source of high average powers (in the kilowatt range) with good beam quality. Good beam quality is necessary to produce the small spot sizes required for industrial applications such as laser welding. Military uses requiring large propagation distances dictate good beam quality also.
Minimal optical distortion in the laser gain media is necessary to achieve good laser beam quality. Several possibilities for corrective measures exist. By meticulously tailoring masks at the slab ends, the optical path variations through the aperture of the slab laser are controlled. This method, however, is fixed operating point dependent and difficult to achieve. Another method is to place corrective optics in the resonator cavity, or to use active mirrors (phase conjugation techniques) which change shape in response to phase errors in the laser wave front. These methods correct beam quality as an afterthought, are difficult and expensive to implement, and introduce considerable additional complexity into otherwise simple systems.
The architecture of the present invention has been described by Kinpui Chan. See "Multipass Laser Diode Pumped Nd: YAG Amplifier Design", Applied Optics, Vol. 26 No. 16, pp. 3177-3179, Aug. 15, 1987. The context of Chan's paper is unrelated to the reduction of beam distortions in solid state slab lasers. Chan's paper is exclusively concerned with multi-pass amplification of miniature lasers. The paper describes an idea only, not the results of an experiment, and does not allude to high average power or continuous-wave operation or associated beam quality problems and their resolutions. Neither Chan nor others working in this field have recognized that a solid state slab laser with square ends will produce an output beam with reduced thermally induced optical distortions. These advantages have been recognized for the first time in the present invention.
It is desirable to have a general method and article capable of producing good laser beam quality from solid state slab lasers by reducing thermally induced optical distortions. The present invention provides such a method and article.